1. Field of the Invention
The present invention relates to a lens driving apparatus for a disc player for recording onto and/or reproducing from a disc, which is a record medium for a CD (Compact Disc), a DVD or the like.
2. Description of the Related Art
There is a lens driving apparatus for a disc player for recording onto and/or reproducing from a disc as a record medium for the CD or the DVD to correspond to a demand for a smaller, lighter and thinner structure The lens driving apparatus can be roughly classified into: a semiconductor optical unit having a light emitting element for emitting a light beam, a grating, a beam splitter, a light receiving device and the like; and an actuator unit having a moving portion. The semiconductor optical unit can be drastically miniaturized by wiring the semiconductor elements such as the light emitting element, the light receiving element and the like in a chip state, and then packaging them together with other optical parts with ceramic or resin member, to thereby make them into a module.
Also, the module into which the optical parts, the semiconductor elements and the like are integrated is produced in a dedicated process. Thus, the assembling accuracy of the optical parts and the like can be improved as compared with a conventional method of assembling respectively the individual parts on a printed substrate or the like. Hence, the performance as the module can be improved to thereby attain the stable performance. Moreover, the modularization of the optical parts is standardized by the miniaturization. Accordingly, the mass production efficiency can be improved to thereby attain the reduction in a cost.
On the other hand, the actuator unit can be drastically miniaturized and its weight can be drastically reduced, for example, by employing a printed substrate coil, in which a copper lamination print substrate in a form of film is etched to form a driving coil, instead of a conventional configuration in which a driving coil, such as a tracking coil, a focus coil or the like, is wrapped around a lens holder of a bobbin type.
The actuator unit is provided with: a magnet; and a moving unit in which a lens holder having the printed substrate coil and the objective lens is movably supported by four elastic bar members. With regard to the actuator unit, although the number of configuration parts is small and the structure is also simple, it has an important role of accurately making a beam spot on an information track on the disc, and also making the moving unit accurately follow a tracking error signal and a focus error signal.
By the way, the printed substrate coil constituting the actuator unit is configured such that a focus coil is typically formed at a center thereof, and that four tracking coils, in which sets composed of upper and lower two elements arranged in a focus direction are disposed on both sides of the focus coil, are formed on a flat surface. In this case, the magnet constituting the actuator unit employs such a structure that magnetic fluxes in directions opposite to each other along a jitter direction are applied to the two coils arranged in the upper portion and the two coils arranged in the lower portion. In the actuator unit having the above-mentioned configuration, if the actuator unit is driven in the focus direction, a rotationally driving force (i.e., the rolling phenomenon) is induced in the printed substrate coil.
If the rotationally driving force is induced, the actuator unit cannot make the moving unit accurately follow the tracking error signal or the focus error signal. Thus, the actuator unit requires an operation for canceling such a rotationally driving force. The method of canceling the rotationally driving force may be considered in which the actuator unit uses two kinds of printed substrate coils whose pattern shapes are different from each other and a pair of magnets, which are constituted correspondingly to these printed substrate coils and which are multi-polar-magnetized. However, by this method, it is difficult or impossible to reserve the space to newly add a part for canceling the rotationally driving force, and this runs counter to the standardization and the part saving configuration.